Variadic function: Difference between revisions

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===In C===

To portably implement variadic functions in the [[C (programming language)|C language]], the standard [[stdarg.h|{{code|stdarg.h}}]] header file is used. The older [[varargs.h|{{code|varargs.h}}]] header has been [[Deprecation|deprecated]] in favor of {{code|stdarg.h}}. In C++, the header file {{code|cstdarg}} is used.<ref>{{cite web|url=http://www.cplusplus.com/reference/clibrary/cstdarg/|title=<cstdarg> (stdarg.h) - C++ Reference|website=www.cplusplus.com|access-date=2007-10-02|archive-date=2012-10-31|archive-url=https://web.archive.org/web/20121031160547/http://www.cplusplus.com/reference/clibrary/cstdarg/|url-status=dead}}</ref>

<syntaxhighlight lang="C">

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The [[CERT Coding Standards]] for C++ strongly prefers the use of [[variadic templates]] (parameter pack) in C++ over the C-style variadic function due to a lower risk of misuse.<ref>{{cite web |title=DCL50-CPP. Do not define a C-style variadic function |url=https://wiki.sei.cmu.edu/confluence/display/cplusplus/DCL50-CPP}}</ref>

=== In Fortran ===

Since the Fortran 90 revision, [[Fortran]] functions or subroutines can accept optional arguments:<ref>{{Cite web |title=Optional Arguments |url=https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2023-0/optional-arguments.html |access-date=2025-03-18 |website=Intel |language=en}}</ref> the argument list is still fixed, but the ones that have the {{code|optional}} attribute can be omitted in the function/subroutine call. The intrinsic function {{code|present()}} can be used to detect the presence of an optional argument. The optional arguments can appear anywhere in the argument list.

<syntaxhighlight lang="fortran">program test

implicit none

real :: x

!> all arguments are passed:

call foo( 1, 2, 3.0, 4, x )

!< outputs 1 \ 2 \ 3.0 \ 4 \ 6.0 (the "\" denotes a newline)

!> the last 2 arguments are omitted:

call foo( 1, 2, 3.0 )

!< outputs 1 \ 2 \ 3.0

!> the 2nd and 4th arguments are omitted: the arguments that are positioned after

!> an omitted argument must be passed with a keyword:

call foo( 1, c=3.0, e=x )

!< outputs 1 \ 3.0 \ 6.0

!> alternatively, the Fortran 2023 revision has introduced the .NIL. pseudo constant

!> to denote an omitted argument

call foo( 1, .NIL., 3.0, .NIL., x )

!< outputs 1 \ 3.0 \ 6.0

contains

!> the subroutine foo() has 2 mandatory and 3 optional arguments

subroutine foo( a, b, c, d, e )

integer, intent(in) :: a

integer, intent(in), optional :: b

real, intent(in) :: c

integer, intent(in), optional :: d

real, intent(out), optional :: e

print*, a

if (present(b)) print*, b

print*, c

if (present(d)) print*, d

if (present(e)) then

e = 2*c

print*, c

end if

end subroutine

end program</syntaxhighlight>

'''Output:'''

<pre>

The sum of [1 2] is 3

The sum of [1 2 3] is 6

The sum of [1 2 3 4] is 10

</pre>

===In Go===